Posterior mediastinum

Question 1

State the contents of the posterior mediastinum

Answer 1

DATES

1. Descending aorta
2. Azygos and hemiazygos veins
3. Thoracic duct
4. Esophagus
5. Sympathetic trunk

Question 2

Describe the position of the oesophagus

Answer 2

Runs from pharynx to stomach, specifically from the inferior border of cricoid cartilage (opposite C6)-> t11

It passes through the oesophageal hiatus at T10

On its right is the thoracic duct and on its left is the descending aorta

Question 3

Describe the arterial supply, venous/lymph drainage and innervation of the oesophagus

Answer 3

Arterial supply:
Oesophageal arteries which arise from thoracic aorta
Bronchial arteries
Descending branches of lower gastric artery

Venous drainage:
Azygos and hemiazygos veins
Oesophageal branches to lower gastric vein

Lymph drainage: posterior mediastinal and gastric nodes

Innervation: branches arise from vagus and sympathetic trunk

Question 4

Describe the descending (thoracic) aorta

Answer 4

Descends from T5-T12
Enters abdomen via aortic hiatus
Thoracic duct and azygos vein on RHS, also pass through aortic hiatus
Branches: bronchial, intercostal, subcostal, pericardial, oesophageal and superior phrenic arteries

Question 5

Describe the collateral circulatory pathway that can occur if the IVC becomes blocked

Answer 5

The azygos vein can return blood from lower peripheries into SVC

Question 6

Describe the azygos vein

Answer 6

On RHS
Begins at L1/L2 at junction between R.ascending lumbar vein and R.subcostak vein or by IVC
Enters thorax through aortic hiatus
At TTP enters SVC

Tributaries include: right superior intercostal vein, 5-11th posterior intercostal veins, hemiazygos, accessory hemiazygos, oesophageal, mediastinal, pericardial, R.bronchial

Question 7

Describe the hemiazygos

Answer 7

on LHS
Runs from T6 plane
Arises at same junction as azygos
Enters thorax through leeft crus of diaphragm or aortic hiatus

Tributaries
T9-T11 let posterior intercostal veins, oesophageal and mediastinal veins

Question 8

Describe the accessory hemiazygos

Answer 8

on LHS
Not always present
Descends to T8 where it dumps blood into azygos or hemiazygos
Usually has connection to left superior intercostal vein

Tributaries: 4th-8th left posterior intercostal veins, left bronchial veins

Question 9

Describe the thoracic duct

Answer 9

Largest lymph channel
Drains left head, left arm and legs Right lymphatic duct drains rest)
Originates in cisternae chill at L2
Ascends through aortic hiatus
Drains into venous system at left venous angles (between subclavian and internal jugular vein)

Question 10

Describe the segmentation of the sympathetic trunk

Answer 10

T1-T4 are the upper thoracic splanchnic nerves
T5-T12 are the lower thoracic splanchnic nerves

ThE LTSN can be further divided into greater splanchnic nerves (T5-T9), lesser splanchnic nerves (T10/T11) and least splanchnic nerve (T12). They all descend and pierce the diaphragm at the crura

Question 11

Describe how the upper thoracic splanchnic nerves work

Answer 11

Preganglionic fibres exit spinal chord via white rami communicates

Synapse at the ganglia

Post ganglionic sympathetic fibres exit via trunk though grey rami communicates

They then give off branches to cardiac, pulmonary and oesophageal plexi
They also carry from afferent sensory neurones to CNS

Question 12

Describe how to lower thoracic splanchnic nerves work

Answer 12

Preganglionic fibres exit spinal chord via white rami communicates

Pass through ganglia without synapsing

Preganglionic fibres (sympathetic) leave ganglia and pass to abdominal viscera

Carry afferent sensory neurones from abdomen to CNS